Relayless switching circuit for application of ringing signals

ABSTRACT

A relayless switching circuit which provides an effectively open circuit between a telephone and a ringing generator when the ringing generator is de-energized and which is conditioned when the ringing generator is turned on to couple pulses of ringing voltage to the telephone and to effectively open the talking circuit during the occurrences of the ringing voltage pulses.

United States Patent 11 1 1111 3,898,391

Schwarzer, et al. 1 Aug. 5, 1975 54 TW() STA(;E TIMEDIVISION 3.492.430 1/1970 Vigliante ..179/15AT MULTIPLEX TELEPHONE SYSTEM 3.401.235 9/l968 Corbin ..l79/l5AT 3.311.705 3/l967 Corre l79/l5AT 3.280.265 10/1966 Von Sanden ..l79/15AT [75] lnvemorc l g f g Fiankfurt 3,275,749 9/1966 Kunihiro ..179/15AT am 'f 2.877.304 3/1959 Hagenhaus ..179/15AT Johannes-Georg Schosnig, Frankfurt am Mallh Germany Primary Examiner-Kathleen H. Claffy Assistant Exuminer-Thomas DAmico [73] Assigneez Telefonbau und Normalzeit Attorney. Agent Firm ErWin s G.m.b. H., Frankfurt am Mam. Germany [57] ABSTRACT [22] Filed: Mar. 7, 1973 An improved two-stage time division multiplex system or telephone exchange adapted for four-wire operation. The line terminals are sub-divided according to their functions into groups, each group having, and Mar. 9. 1972 Germany ..P 22 11400.7 being comtolled its group connection Store' The incoming and outgoing hues of each group are connected to separate buses or highways, and the [21 I Appl. No.: 338,779

[30] Foreign Application Priority Data [521 vs. c1 ..179/15 AT; 179/18 J buses or highways of each group y be intercon- 511 1111.0 ..H04J 3 00 hected y gates 9r Coupling points The buses or highways connected to the outgoing lines of all [58] Field of Search 179/15AT. 15A. 15A groups y be connected y gates of Controllable 79 5 5 181 coupling points to the buses or highways to which the incoming lines are connected. The last mentioned l l References Cite coupling points are under the control of bus con- UNITED STATES PATENTS nection stores. Both the group connection stores and the bus connection stores are under the control 3.694.580 9/1972 111656 ..179/15AT a central programmed Computer having a central 3.597.544 3/1971 Kennedy 179/2DP or computer store.

1 Claim, 4 Drawing Figures A-KS (first coupling (secorsd coupling stage) 51 stage f B-SSI TN inter-bus (group of subscrib (8-552 l Q0 5 stationes) Q ves2 BKP 3 roup onnection zhhh VSP-SS storage control storage control ZBK P cgnnection (supervisory channel) K K 5 ores PATENTEB 51975 3,898,391

SllEEl 1 OF 4 FlG.l

subscriber terminal equipment (group of subscriber stations) (first coupling stage) TNG subscriber TSS WR WS SS selection E} W( A-KS register AT 1 dial t t register s a e scanner l: I SL6 (special lines group) second tie line tie lines repeater $5 coupling N ,-Q-U v stage Ll A-KS PBX line NAL-Ue line circuit AT J state scanner PBXlines central control (special group) SS Computer station Q SR line circuV BP I switchboard L BPS line circuit KSt (supervisory channel central channel control PATENTEU 5W5 898,391

SHLU 2 BF 4 FIG. 2

A-KS B-KS (first coupling (secon)d Coupling stage) 31 stage 65 d f B-SS'! inter-bus TN l BKP gates (group of subscriber stationes) A-SS2 v) group I connection store K K/ VSP-SS storage Jf control storage control L ZBK bus P" cgnnectlon s (Supervisory channel) K K ores PATEHTED AUG amplitude sample transmitter APS'l Siiii 3 SF 4 FIG.3

V651 (group switching device) 65R J voice bus BKP1 voice bus ves2 Q APE2 I amplitude sample receiver amplitude sample transmitter APS3 (group switching BKP3 inter-bus gate BKP gate

V653 (group switching device) -BKP6 V684 inter-bus (group switching gate device) 5 inter-bus gate amplitude sample receiver I PGS(interface) register KKSt KK i (channel head) J AK(output channel) (input channel) BAL(block address channel lines) StL (control lines) ZBK A channel head register V (supervisory channel) An St selector 000cc dd I (channel control) l l register J l l l Reg KSt AnPE conversion device SR5 (interface) TWO-STAGE TIME-DIVISION MULTIPLEX TELEPHONE SYSTEM BACKGROUND OF THE INVENTION In prior art time-division multiplex telephone systems the number of connections which may be established and maintained simultaneously over one single bus or highway is limited by the electrical properties of the bus or highway, and the switching speed of the connection means to a number in the order of about 100. Since there is often a need for establishing and maintaining a larger number of simultaneous connections, it is necessary to expand time-division multiplex systems in such a way as to cope with high traffic density requirements. As long as multiplexing is effected in but one stage, the number of coupling points must be increased,

resulting in systems having a plurality of buses or I highways instead of but one. In view of the limitations and drawbacks of such systems it is generally more desirable to resort to multi-stage time-division multiplex systems.

One prior art multistage time-division multiplex system is limited to two-wire operation, and cannot Y readily be adapted for four-wire operation.

The Highgate Wood experimental electronic telephone exchange system installed in North London, England, lends itself to four-wire operation, and has means for multi-stage time-division multiplexing. In that system the external lines are arranged in groups and all the lines in one group are connected by gates to a pair of group highways or buses, one for each direction of transmission. Each pair of group highways or group buses can be interconnected by an inter-group gate, or inter-group coupling point. In other words, the in-highway and the out-highway of each group can be connected by an inter-group gate, or inter-group coupling point. The invention relates to a greatly improved version of the aforementioned experimental system.

SUMMARY OF THE INVENTION One concept underlying the present invention is to effect the control of groups of peripheral devices such as groups of subscriber terminals, groups ofAL- QL, and NAL lines, and groups of switchboards and data transmission terminals preponderatly by peripheral devices, and to assign only control operations of a higher order to a programmed digital computer in the central exchange.

According to this invention the external lines are arranged in groups depending upon function, i.e. subscriber station groups, special line groups and special groups. Each of these groups is provided with, and operatively related to, a group connection store. A bus connection store is provided for, and operatively related to, each in-bus (or in-highway) or out-bus (or out-highway) of each group. The bus connection store connects the various out-buses and in-buses ofthe particular groups by means ofcoupling points with other in-buses and out-buses. The aforementioned group connection stores as well as the aforementioned bus connection stores are controlled over a particular channel system by a central digital computer, or by a corresponding programmable centrally located system.

In telephone systems embodying the present invention the aforementioned functional terminal or line groups form separate units which require but a relatively limited number of lines for their connection to the centrally located coupling stage and the centrally located system control. This is of particular importance in instances of time-division multiplex systems which extend over large areas.

Another desirable feature of systems embodying the present invention resides in the fact that the pulse density in the long buses or highways and in the central coupling stage is but half as large as in the remote spatially concentrated terminal groups.

Still another desirable feature of systems embodying the present invention resides in the fact that the central control computer has but decision making functions all effectuating functions being carried out outside in decentralized equipment.

Systems embodying the present invention are particularly applicable in instances where flexibility is of the essence, and further expansion thereof is contemplated.

BRIEF DESCRIPTION OF THE DRAWINGS DESCRIPTION OF PREFERRED EM BODI MENT Referring now to FIG. 1, reference character A- KS has been applied to indicate the "first coupling stage and reference character B-KS has been applied to indicate the second coupling stage of a timemultiplex system having two stages. The first coupling stage A-KS includes several groups as, for instance, groups TNG of subscriber stations, special line groups SLG and special groups SNG. FIG. 1 shows by way of example but one of each of the aforementioned groups. The groups TNG of subscriber stations, of which there may be many, depending upon the system under consideration, serve the purpose of connecting subscriber stations TSS by the intermediary of subscriber terminal equipment TS to the coupling stage A-KS. The individual voice channels extend from the subscriber stations TSS to the coupling stage A-KS. but the state of the subscriber stations TSS (e.g. idle or busy) is determined by a state scanner AT and a corresponding signal is transmitted by way of the state and control signal transmission path ZBK and channel control KSt for said path to the centrally located digital control computer SR. The latter transmits control signals by the intermediary of the state and control signal transmission path to the coupling stages A-KS and B-KS. Both coupling stages A-KS and B-KS are interconnected by the voice buses SS, and establish the desired new connections on the basis of the control Signals being received by them.

Reference character WR has been applied to indicate a dial register which receives and stores dialed information and transmits the same by the intervmediary of the dialed information circuitry WS to the coupling stage A-KS.

In a similar fashion special lines groups SLG are connected to the coupling stage A-KS. The special lines groups SLG include leased tie lines, and extension station or PBX lines NAL-Ue, respectively. Reference character Q Ue has been applied to indicate a leased tie line repeater for connecting a leased tie line, to coupling A-KS. As a general rule the density of traffic in the lines pertaining to groups SLG is larger and the number of such connections is smaller than those ingroups TNG of subscriber stations. I

The special groups SNG include switchboards BP and special telecommunication devices as, for instance, conference call devices, data stations DS or picture phone stations which are connected by the intermediary of appropriate intermediary circuitry BPS and D85 to thecoupling stage A-KS.

All coupling stages A-KS are alike, except that special groups SNG call for wide band transmission.

Referring now to FIG. 2, coupling stages A-KS and B-KS are shown therein in greater detail. The subscriber station TS is connected by four-wire lines to voice buses A-SSl and A-SSZ by the intermediary of amplitude sample transmitters APS and amplitude sample receivers APE. There are connections whose origin and termination pertain to the same group. In order to establish such connections voice buses A-SSl and A-SS2 may be interconnected by the group switching device GS. Establishing connections between different groups of lines involves the coupling stage B-KS. To this end the voice buses A-SSl and A-SS2 may be interconnected by group connection switching devices VGSl and VGS2 with corresponding voice buses B-SSl and B-SS2, respectively. Reference character BKP has been applied to indicate switching devices for connecting the aforementioned busesB-SSI and B-SS2 of the coupling stage B- KS shown in FIG. 2 with the corresponding buses of coupling stage B-KS of other groups of lines which are not shown in FIG. 2. The coupling stage B-KS shown in FIG. 2 is structured in such a way that the transmitting voice buses of one groupe.g. buses 3-851 and 3-582 of a group TNG of subscriber stations-can be connected to the receiving voice buses of all other groups by the intermediary of one of a plurality of switching devices BKP.

APS, the control of the amplitude sample receiver APE, the control of the group switching device GS and that of the group connection switching devices V081 and VGSZ is effected by means of the storage control system Sp-St and group connection storage device VSP-G. The control of coupling points BKP is effected by bus connection storeVS PeSS.

Referring now to FIG. 3 it will be explained more in detail in connection with that figure how a connection is established between terminal stations pertaining to the same group and how a connection is established between terminal stations pertaining to different groups. FIG. 3 shows portions ofa coupling stage A-KS and of a coupling stage B-KS shown more in detail in FIGS. 1 and 2 and described inconnection with these two figures. The system shown is one without change of phase, i.e. a certain fixed phase within a larger interval of time is assigned to a givenconnection during which phase information is transmitted in either of both directions. Considering connections between the same group, the two signals are transmitted sequentially over 'the same message path. On the other hand, considering connections between two different groups, in that instance parallel transmission is effected via two different message paths. This will be explained below in more detail. 7

Assuming that it is intended to interconnect two lines U, and U pertaining to the same group U. The fixed phase or interval of time assigned to this specific connection is subdivided into two parts. During the first part of the aforementioned phase or interval of time information is transmitted from line ,U, by the intermediary of amplitude sample transmitter APSl, the group-switching device 681, the amplitude sample receiver APE2 to, the line U During the second part of the aforementioned phase or interval of time information is transmitted from line U2 by the intermediary'of amplitude sample transmitter APSI, the group switching device G81, and the amplitude sample receiver APEl to the line U,. It is thus apparent that two amplitude samples are transmitted within one complete phase or interval of time as, for instance, by the intermediary of group switching device 081.

Considering now the case of establishing a connection between lines U, and V, which pertain to different groups In that instance information is. transmitted in another fashion than in the instance which has been considered above. In the case or instance of a connection between lines U, and V, pertaining to different groups information is transmitted within 'the same phase or interval of time fromline U,

by the intermediary of amplitude sample transmitter APSl, the group connection switching device VGSI, the coupling point BKPS, the group connection switching device V054 and the amplitude sample receiver APE3 to line Vl, while information is transmitted from lines V, by the intermediary of amplitude sample transmitter APS3, the group. connection switching device VGS3, the coupling point BKP2, the group connection switching device V652 and the amplitude sample .receiver APSI to line U,.

It will be apparent from the abovethat the pulse density along all elements forming the communication channel is only half of the pulse density which prevails when lines are interconnected which pertain to the same group. Since the length of a communication channel established between two different groups is generally longer than the length of an intragroup communication channel. this tends to result in undesirable secondary effects which can be avoided by increasing the spacing between pulses.

As shown in FIG. 1 the coupling stages A-KS and B-KS are connected to the central control computer SR by the intermediary of the state and control channel ZBK and the channel control KSt. The adaptation of the peripheral devices to the aforementioned channel is effected by channel heads KK. This is illustrated in FIG. 4 andwill be described below more in detail.

The state and control channel ZBK includes an input channel EK for serially transmitting information regarding states in central direction. an output channel AK for serially transmitting control signals in a direction opposite to said central direction. block address lines BAL for selecting individual channel heads KK and control lines StL for controlling transmission conditions. The channel heads KK and the channel control KSt include registers Reg.KSt and Reg.KK. respectively. for storing signals relating to state and supervisory control. Writing into the aforementioned registers and readout thereof. respectively. is effected in channel heads KK by means of peripheral devices such as. for instance. the group connection storage device VSP-G (FIG. 2). by the intermediary of parallel interface device PGS. On the other hand. the transmission between channel heads KK and the centrally arranged channel control KSt is effected serially. The output process is initiated by the central control computer SR. The output control or supervisory signal is transmitted through interface device SRS to channel control KSt. That signal includes a control or supervisory code signal proper. transmitted by conversion device AnPE to the register Reg. KSt and the address of the channel head intended to be reached. The term conversion device as used in this context is intended to refer to means for modifying in one way or another information transmitted to. or from. the central control computer. Such a conversion may consist in a change of speed. a series to parallel conversion or of a change of coding. The address of the channel head intended to be reached is initially received by block address register BL Reg. and is transmitted from there by block address line BAL to the respective channel head KK. The selector AnSt and the control lines StL initiate the transmission process by which the content of register Reg.KSt is transmitted serially by means of output channel AK to the register Reg.KK of the selected channel head KK. Said content is then transmitted in parallel by way of the interface device PGS to the device to be controlled. The input is effected in a similar fashion. Since the address of the channel head KK which is in a state of readiness is initially not known to the channel control KSt. a scanning process is initiated involving a step-by-step change of the address register BL Reg. until a change of state is noted by input channel EK. Only then is this signal serially transmitted to the channel control KSt and placed into the control computer SR. jointly with the address ofthe corresponding channel head.

As is apparent from the above the object of the channel system-Le. the individual channel heads KK. the state signal and the control signal communication channel ZBK and the channel control KSt is to transmit state indicating signals and control or supervisory signals between the periphery of the system and itscentral unit. This may be further illustrated by the following example.

When an idle subscriber goes off-hook. the scanning device AT of the group of subscriber stations to which the particular subscriber belongs senses the change of state from idle to busy. This change of state signal is combined with a tag signal indicating whether the calling subscriber station is a conventional dialing station. a key dialing station, a data transmitting and receiving station, a picture telephone station. etc., to a unitary message and transmitted to the central unit by way of a channel head KK, a signal channel and channel control KSt. The message is processed in the central control unit. To this end a clear or empty line is seized and reserved in the central call record. Further a search is made for a clear line in the selection register WR. As a result of the operations in the central unit, a supervisory order for the respective group of subscribers is assembled. This supervisory order transmitted to connection storage VSP-G by the channel system includes the number of the connection line in the connection storage VSP-G to be seized, the number of the subscriber station TSS. the number of the selection register WR and a control signal for processing the call. The number of the subscriber station. the number of the selection register and the control signal are recorded in the addressed line of the storage control system Sp-St. In the instant case the above referred-to control signal results in that the transmission end of the subscriber station is periodically connected to the selection register WR. and that its receiving end is supplied with a dialing tone.

The operational task of the central unit is completed when it has assembled the supervisory order. The operational task of the channel control KSt is terminated when it transmits the supervisory order to the channel head KK. The latter is freed or idled when the storage control system Sp-St has received the order. Finally. the operational task of the storage control system Sp-St is completed when a record is placed in the particular storage line of the storage control system. This mode of independent operation of the central unit. the channel control KSt, the the channel heads RR and the peripheral storage control units Sp-St makes it possible to optimize the distribution of the load, and to achieve a reasonable balance among the various speeds of operation.

The central control computer RS may be either a general purpose computer or a special purpose computer with programmed control and central storage or memory.

I claim as my invention:

1. A two stage time-division multiplex telephone system including a. external lines connecting amplitude sample transmitters (ASP) and amplitude sample receivers (APE) with first stage outgoing and incoming buses (A-SSl, A-SS2). said external lines being arranged in equal function groups 7 a V (TNG, SLG. SNG), and external lines pertaining to the same of said equal function groups being connected to a pair of said first stage outgoing and incoming buses;

' first coupling points (GS) each for interconpairs of second stage outgoing and incoming buses (8-881, 8-552);

. pairs of group switching devices (VCiSl), VGS2),

each pair of said pairs of group switching devices being interposed between a pair of said first stage outgoing and incoming buses (A-SSl;

A-SS2), and a pair of said second stage outgoing and incoming buses (BSS1, 8-582), and said pairs of group switching devices (V081, V052) being under the controlof said group connection stores (VSP-G);

. a plurality of pairs of second coupling points (BKPI, BKP2, BKP3, each of said plurality of pairs of second coupling 'points being arranged to interconnect a pair of said second stage outgoing and incoming buses (8-851, 8-882) and being under the control of one of a plurality of bus connection stores (VSP-SS) to establish four wire connections between pairs of said externallines of different of said equal function groups (TNG, SLG, SNG); and

.a channel system transmitting control data connectingsaid group'connection stores (VSP- G) and said bus connection stores (VSP-SS) to a central programmed control computer (SR). 

1. In combination with a telephone, a talking circuit normally connected to said telephone, a telephone transmission line providing a signal-transmitting connection between said talking circuit and a central office, and a ringing generator located at the talking circuit end of said transmission line remote from said central office for developingg an a.c. voltage in response to the occurrence of a pre-selected signal which is transmitted from said central office to signal an incoming call to said telephone, a static switching circuit rendered effective by said a.c. voltage (a) to convert said a.c. voltage into a pulsating d.c. ringing voltage and to apply said pulsating ringing voltage to said telephone to operate a signaling device in said telephone and (b) to effectively electrically disconnect a portion of said talking circuit from said telephone during application of the pulses of said ringing voltage to said telephone.
 2. In combination with a telephone, a signal transmitting circuit having an interface transformer, a winding forming a part of said transformer, and a ringing generator which is responsive to a pre-selected signal to produce an a.c. voltage, a switching circuit having first and second semiconductor means, and first semiconductor means being in series with said winding in a first circuit branch, said second semiconductor means being in series with said generator in a second circuit branch, and said first and second circuit branches being connected in parallel across operating terminals of said telephone, said second semiconductor means being effective to couple d.c. ringing voltage pulses to said operating terminals only on the occurrence of half cycles of only one pre-selected polarity of said a.c. voltage, and said first semiconductor means being effective upon the occurrence of said d.c. pulses to effectively open the circuit which connects said first branch across said operating terminals.
 3. The combination defined in claim 2 wherein said first and second semiconductor means respectively are a diode and a Zener diode.
 4. The combination defined in claim 3 wherein a terminal of a battery is connected to said generator, wherein said switching circuit further comprises a capacitor connected in said second circuit branch in series with and between said Zener diode and said generator, and wherein a further diode has one terminal connected to a junction between said capacitor and said Zener diode and its other terminal connected to a junction between said generator and said battery to effect the charging of said capacitor only during half cycles of said a.c. voltage which are of the opposite polarity from said one pre-selected polarity.
 5. A telephone tranmission system comprising signal transmission means, a telephone instrument, a transformer normally coupling said telephone to said transmission means and having first and second winding means, said first winding means being connected to said transmission means, a ringing generator energizable from an inactive state to an active voltage-producing state by a pre-selected ring control signal, and circuit means for connecting said generator to said telephone to couple pulses of ringing voltage to said telephone, said circuit means including a semiconductor device which is normally conductive when Said generator is in said inactive state to complete a signal transmitting circuit between second winding means and said telephone, the bias of said semiconductor device being controlled by voltage conditions which are developed when said generator is in its active voltage-producing state to effectively open said signal transmitting circuit during the occurrence of said pulses.
 6. The telephone transmission system defined in claim 5 wherein said transmission means comprises a carrier circuit.
 7. The telephone transmission system defined in claim 5 wherein said circuit means further comprises a capacitor connected in series with said generator and a Zener diode connected in series with said capacitor and said generator, said semiconductor device being in parallel with the circuit branch containing said generator, and Zener diode and said capacitor.
 8. The telephone transmission system defined in claim 7 wherein a battery is connected to said second winding means, and wherein said circuit means further includes a semiconductor diode, the positive terminal of said battery being connected through said semiconductor diode to interconnected terminals of said Zener diode and said capacitor.
 9. The telephone transmission system defined in claim 8 wherein said semiconductor device is a semiconductor diode, said battery, said second winding means, and said semiconductor device being connected in series in a circuit branch which is connected across terminals of said telephone.
 10. In combination with a telephone, a telephone transmission line adapted to be connected to a central office, a talking circuit normally electrically connected to said telephone to provide a signal-transmitting connection between said telephone and said transmission line, and a normally de-activated ringing generator located at the talking circuit end of said transmission line remote from said central office, said generator being turned on to develop an a.c. output voltage in response to the occurrence of a pre-selected signal which signals an incoming call to said telephone, the improvement comprising a static switching circuit connected to said generator, said talking circuit and said telephone for maintaining said generator effectively electrically disconnected from said telephone in absence of said output voltage, and said switching circuit being rendered effective by said output voltage (a) to convert said output voltage into a pulsating d.c. ringing voltage and to apply said pulsating ringing voltage to said telephone to operate the telephone''s ringer and (b) to effectively electrically disconnect a portion of said talking circuit from said telephone during application of the pulses of ringing voltage to said telephone.
 11. The combination defined in claim 10 wherein said switching circuit has only passive and two terminal semiconductor components.
 12. The combination defined in claim 10 wherein said talking circuit comprises a transformer having first and second mutually coupled winding means electrically connected to said telephone and said transmission line respectively, and wherein said switching circuit includes a semiconductor component in series with said first winding means and reverse biased by said pulses of ringing voltage.
 13. In combination with a telephone, a telephone transmission line adapted to be connected to a central office, a talking circuit normally electrically connected to said telephone to provide a signal-transmitting connection between said telephone and said transmission line, and a normally de-activated ringing generator located at the talking circuit end of said transmission line remote from said central office, said generator being turned on to develop an a.c. output voltage in response to the occurrence of a pre-selected signal which signals an incoming call to said telephone, the improvement comprising a static switching circuit connected to said generator, said talking circuit and said telephone for maintaining said generator effectively elEctrically disconnected from said talking circuit in absence of said output voltage, and said switching circuit being rendered effective by said output voltage to apply a pulsating d.c. ringing voltage to said telephone to operate the telephone''s ringer.
 14. The combination defined in claim 13 wherein said switching circuit has only passive and two terminal semiconductor components.
 15. The combination defined in claim 13 wherein said generator has a pair of output terminals across which said output voltage is developed, and wherein said switching circuit comprises a capacitor, semiconductor means connected in series with said capacitor across said output terminals to complete a circuit which applies said output voltage to charge and capacitor only on output voltage alternations of one pre-selected polarity, a capacitor discharge circuit branch including a Zener diode, said discharge circuit branch electrically connecting said capacitor to said telephone for discharging said capacitor with a time constant that is longer than the time constant for charging said capacitor, said capacitor being electrically connected between said Zener diode and one of said output terminals so that said output voltage and the charge stored on said capacitor are applied in series for biasing said Zener diode, said Zener diode being biased to its non-conducting state when said charge and said output voltage are opposing and being reversed biased far enough to conduct when said output voltage and said charge are of a common polarity and thus additive to each other to thereby facilitate the application of the ringing voltage pulses to said telephone. 